This invention relates to an explosive composition of the type known as a watergel or a slurry-type composition and to a process for manufacturing this explosive composition.
Watergel or slurry explosives are widely used because they perform well and are relatively safe to make, store and use. The high water content of watergel or slurry explosives has, however, necessitated that they be cartridged in plastic packaging. This has drawbacks in that it has presented difficulties inter alia with the proper loading of the explosive into boreholes.
In South African Patent Application No. 94/2573, an improved watergel or slurry explosive is described which has a sufficiently low water content that it is dry to the touch and can therefore be packaged in standard waxed paper cartridges of the type used for packing dynamite or other nitroglycerine sensitized explosives without causing the paper cartridge to disintegrate. The hydrogel explosive compositions described in South African Patent Application No. 94/2573 are capable of initiation by a number six strength detonator in small diameter cartridges and they are thus said to be "cap sensitive in small diameter" cartridges.
The cap sensitivity of an explosive composition is a measure of the reliability of detonation of the explosive composition in the field. The lower the temperature at which an explosive composition is cap sensitive, the less prone it is to transient desensitisation and the more likely it is to detonate reliably in the field. Also, the smaller the diameter of the cartridge, the more difficult it is to achieve cap sensitivity at a low temperature. A perchlorate salt or pigment aluminium is incorporated into the explosive compositions described in South African Patent Application No. 94/2573 to make them cap sensitive in small diameter at temperatures of 5.degree. C. or less as these components are known to lower the temperature at which an explosive composition is cap sensitive.
While the inclusion of a perchlorate salt or pigment aluminium in an explosive composition improves cap sensitivity of the composition and thus enhances its reliability, there are certain drawbacks to the inclusion of these components.
In certain countries, such as South Africa, perchlorate salts and pigment aluminium are expensive. Perchlorate salts are also very reactive.
Therefore, while the inclusion of a perchlorate salt enhances the cap sensitivity of a composition containing it, it also increases the frictional and impact or shock sensitivity of the composition. This makes the composition relatively less safe to make, store, transport and use. However, it has not been possible to do away with the perchlorate salt or pigment aluminium and still achieve low temperature cap sensitivity in these low water watergel compositions when packaged in small diameter.